A new pesticide which some scientists have likened to DDT will not be registered in the United States for use on cotton fields, the Environmental Protection Agency (EPA) announced Wednesday. According to the agency, studies have shown that the chemical, chlorfenapyr, is "persistent in the environment and causes severe effects on bird reproduction." Chlorfenapyr's maker, New Jersey-based American Cyanamid, disputes EPA's characterization of the pesticide.

American Cyanamid wanted EPA to register chlorfenapyr--better known under its trade name "Pirate"--for use against beat army worms, pests which periodically wreak havoc in the nation's cotton fields. Until recently, there was little defense against the insects; pending the outcome of EPA-ordered studies, chlorfenapyr has been used under emergency exemptions on millions of cotton acres in the United States over the last 5 years.

Pirate is a member of a class of chemicals called pyrroles, which kill by tampering with several enzymes needed to manufacture the energy storage molecule ATP in cells' mitochondria. American Cyanamid claims that chlorfenapyr specifically acts on enzymes that are abundant in insects, leaving other organisms unharmed. It adds that no one has yet found any ecological damage attributable to the chemical.

But environmentalists and some scientists claim that Pirate, like DDT, builds up in the environment and accumulates higher up in the food chain, where it can do damage. In an EPA-mandated lab study by American Cyanamid, for instance, mallard ducks fed chlorfenapyr laid fewer eggs than controls, and fewer of those eggs hatched. But the company says this trial paints an unrealistic picture of the risk of chlorfenapyr, arguing, among other things, that the ducks were fed larger amounts of Pirate than they could ever consume in the wild.

A spokesperson for American Cyanamid says that the company may file new applications for EPA approval in the future and that the withdrawal should not be seen as an admission that the product has toxic effects. "We'll be back on this," she says. Although satisfied with the decision, environmental groups say they are girding for a long fight. "This is only the first win," says Kelley R. Tucker of the Washington-based American Bird Conservancy, which spearheaded a year-long campaign to derail Pirate. "We're going to continue to watch chlorfenapyr like a hawk."